The Mars Science Laboratory rover, Curiosity, is set to touch down in a few hours – 1:31am EDT (05:31 UTC). How It Works magazine spoke to the NASA brain behind the mission, project scientist Dr. John Grotzinger. You can read all about the MSL mission in our big feature in issue 36 of How It Works magazine.

How It Works: What’s your role as project scientist on the MSL?

John Grotzinger: Probably the best way to think about it is like being the chief scientist. What that means is that we’ve got the rover and all its capabilities and all the science instruments, ten science instruments and nine principal investigators who were responsible for building it and developing those instruments, calibrating them and establishing protocols and procedures for how we’re going to operate them when we land on Mars. My responsibility is to co-ordinate all this interaction and oversee the science team of 300-plus team members.

Gale Crater - where the Curiosity rover will land and begin its investigation as to whether Mars was once habitable for life.

HIW: Your area of expertise is “Ancient surface processes on Earth and Mars” – we’d imagine you provide insight into that specific area as well?

JG:Yeah. Basically, since the primary objective for the mission is the search for habitable environments on Mars – and the emphasis is strongly in the area of ancient Mars, which is why we chose the landing site – it’s kinda exactly what I do on Earth. So as a geobiologist, before I got involved in Mars projects, we head off into a particular field area that we select in advance usually involving some of the oldest rocks on Earth. Then we set up our equipment, make maps and collect samples that we bring back to the lab for analysis. So if you ask the question ‘how does one go about exploring for a habitable environment?’ these are the sorts of things that I typically do on Earth in a very analogous way.

HIW: So how do you go about investigating life on another planet?

JG: What we do is borrow quite heavily from these principles and use them for our guidance. The search for a habitable environment involves trying to look for evidence of an aqueous environment because water is important for all microbes. You’re often trying to establish some source of energy that, if the microbes had been there they would have utilized for their metabolism. Then you’re looking for carbon because carbon is a building block for life as we know it. So you take those elements as the key ingredients for life along with some other ‘proper’ elements like nitrogen, hydrogen, oxygen, sulphur and phosphorus that we can characterize using our instruments. Then you’re looking for the geological context that can present those to you. So in the case of looking at layered rocks, what we know on Earth is that when we go through thick sequences of sedimentary rocks, we know that some environments are more habitable than others and some might represent ancient deposits that might have been formed in quite dry or arid environments. We see that alternate with the kind of ancient deposits that might have formed, in the case of Earth, a marine environment. What we hope is that, as we work our way up through the layers at Mount Sharp in Gale Crater we’ll be able to characterize those layers and look for the physical properties and chemical properties that tell us about what kind of ancient environment this was.

“I just can’t see any particular reason why [life] might not have happened.” – John Grotzinger, MSL Project Scientist

On MER (Mars Exploration Rover) we learned at Meridiani that there were ancient sand dune environments but there were also ancient environments where there was water flowing across the surface: shallow streams as we reconstructed it to be. So we’ll do the same thing, but at Meridiani we were only able to do about 20 metres of stratigraphy – stratigraphy is a generic word for a succession of layered rocks – but at Gale in the first two years we’re hoping to do literally hundreds of metres. When you do that you get more chances at a discovery of a habitable environment.

The Atlas rocket that launched the MSL capsule into Earth orbit and on its way to Mars.

HIW: Are you able to do more just because of the technology on the Curiosity or because of the geology of Gale Crater?

JG: I think it’s because we have a more capable rover and because we have one of the thickest stratigraphic sections anywhere on Mars that we could explore. So it’s a beautiful combination of advanced technology plus a geological field area that just gives you a lot of stuff to look at.

HIW: Is water the first thing you look for, for evidence of life, or is there something else more fundamental?

JG: I think water is a really appropriate starting point and for us it’s the reason we selected the landing site is because from orbit you can see both mineralogical and geomorphic evidence that there had been water there in the past. MER proved to us that with two rovers and two different places that we can predict where these aqueous places are from orbit. Since MER our ability to do it from orbit has gone up dramatically, so we see large parts of the planets now that were covered with aqueous environments. That doesn’t necessarily mean that it was a habitable environment, but if you don’t have evidence for water, it is sort of the sine quo non for the whole basis of life: if you don’t have water, you don’t have anything for life as we know it.

And then after that things follow thereafter. Ideally you find the kinds of nutrients and elements that life would utilise as energy sources. If you’ve got carbon-based life you’re looking for carbon, but that’s the brilliant thing about our final four landing site: all of them we made very particular predictions about where various aqueous environments were. At Gale we predicted the greatest diversity, so any one of those could give us a habitable environment.

A snapshot of one of NASA's previous Mars rovers - Opportunity - discovering evidence of water on Mars.

HIW: It’s still not certain how Gale Crater formed, yes?

JG: We have a number of different hypotheses about how it formed and truthfully I don’t think there are any from-runners. All we know for sure is that there was an impact a long, long time ago. Within that it filled up with sedimentary materials that possibly went on to filling the entire crater. Subsequent to that filling event it became partially exhumed and it sort of scoured out a moat that leaves a mountain in the middle today. Other than that we don’t really have much of an idea about how that could have formed.

HIW: So millions of years ago the atmosphere and geology of Mars was different to what it is now.

JG: One thing about this is – that may seem a bit odd – we’re not really interested or care about why Mount Sharp got eroded into the shape that it did, we only care that the mountain exists [laughs]. It’s like saying, if you go back and look at the geobiology on Earth, people who went down the Grand Canyon – John Wesley Powell – they had no idea what they were going to find. But basically the geologists who came along discovered trilobites in the lower layers of the Grand Canyon. So you have the beginnings of recognition that layered rocks in the Western US become powerful repositories of early life on Earth. You don’t care that the Grand Canyon cut down into it, you care that doing so it exposed this beautiful archive.

We do, definitely have people on our science team who are interested to try to find out why Mount Sharp formed the way that it did, but most of us are primarily interested in that it just formed an archive that’s been beautifully exposed by the erosion.

To land the Curiosity Rover on Mars, NASA is employing this completely new, rocket-boosted delivery system.

HIW: Speaking more generally about the MSL mission, what sort of things do you expect to find? What would be the dream situation?

JG: Well, what would really be a great mission for us would be that… the rover is able to document on almost a layer by layer basis the early history of Mars’ environment in a more specific way than we’ve ever known before. You have this general sense that the early history of Mars was perhaps wetter and environmentally different than the surface of Mars is today, but the neat thing about reading a successive layer of rocks is that it’s like reading a novel: every layer is a different page in the book and as we work our way up through the succession, we’re sort of turning through the pages and chapters, discovering and interpreting different parts of Mars. So for me, what would make a really great mission would be to go up through this, read the story and realise that Mars was a different planet and specifically, how it was different. All wrapped up in that is if we can find a habitable environment. But it would be even better if we can find out what kind of environments those were.

HIW: So, the burning question – sorry if it’s a bit crass but we have to ask – do you believe that life ever existed on Mars?

JG: [laughs] You know, it’s difficult for someone who’s worked for so many decades on the early history of life on Earth… it seems impossible for me to believe that you can rule it straight out. That puts me ahead of a lot of other people I suppose – I just can’t see any particular reason why it might not have happened. On the other hand, when you look at the evolution of life on Earth you have to realise that a great number of special things have to go exactly right.

I don’t pre-condition my feelings about discovery or joy based on finding evidence. This is the pragmatic side of me being the project scientist: I really have to find the greatest thing about the mission would be, even in the absence of the fact that Mars ever developed life, to be able to use it as a looking-glass to better understand our own evolution here on Earth, how life originated, how it got started, why it evolved when it did, how it was that for almost three billion years after life originated we only had micro-organisms and then suddenly advanced animals developed. All those kinds of questions you wonder: what would have happened if this was different? What would have happened if that was different? Mars actually gives us our chance to replay the tape much in the same way that Stephen J. Gould wrote about, and say, ‘We’re going to start out with two planets, basically the same. Now what happened on the one where life never evolved?’ If we can write that story in this mission that would be really great, even if there is or isn’t a discovery of organic carbon.

The Curiosity rover: a much more advanced and bigger brother to its predecessors, Spirit and Opportunity.

HIW: That’s an interesting perspective, that the potential for life on Mars could reflect on the evolution of life on our own planet.

JG: I’ll just elaborate on that: the reason why it’s an interesting perspective is because, even if life didn’t evolve on Mars we know from studying Earth that the chances of actual records being preserved are very small. So here’s a planet that’s teeming with life and after 60 years of looking after the discovery of the first micro-fossil in 1958, there are only a handful of places where this stuff gets preserved. The rest of the time you go and look at these places, look at these rocks and you don’t see anything. Yet you know it was there. What this tells you is that it takes more than a habitable environment. That habitable environment also has to be an environment that preserves organic carbon. Here’s the paradox: the very substance that makes life possible – water – when it circulates as sediments and the sediments get converted into rock, it actually oxidises all the organics and erases the record. So this is a real important reality we know exists because of Earth, I can’t imagine any reason why we wouldn’t have the same impingement on Mars as well. Then one has to look back and say, ‘if it’s going to turn out to be difficult to find organic carbon, what else can you learn about Mars?’ To me that’s where the important lesson of comparitive evolution comes in.